Since 1978, researchers have collected tens of thousands of migratory birds that died after hitting buildings in Chicago during the spring and autumn seasons and conducted a study that documented a staggering decline in size.
A study published on Wednesday involving 70,716 migratory birds that died between 1978 and 2016 in a collision in Chicago, the third largest city in the United States, found volumes have been dwindling since, but the width of the wings has increased.
The findings suggest that warmer climate is shrinking the size of certain species of migratory birds in North America and possibly around the world, the researchers cite the Burjuman rule, which suggests that individuals within a breed become slimmer in warmer areas and larger in colder regions.
“Findings suggest that warmer climate is shrinking the size of migratory birds in North America and possibly around the world”
The study focused on 52 species, most of which are sparrowhawks, breeding in cold areas in North America and spending winter in locations in southern Chicago. The researchers measured and weighed a group that hit the windows of buildings and fell to the ground.
Over the four decades of study, diminishing sizes were observed in all 52 species. Average body mass fell 2.6 percent and leg length decreased 2.4 percent. But the width between the two wings has risen 1.3 percent, possibly to enable birds to travel the long migration with their smaller bodies.
“This means that climate change seems to change the size and shape of these species”, said Brian Weeks, a biologist at the University of Michigan School of Environment and Sustainability and lead researcher in the journal Ecology Letters.
“Everyone really agrees that the climate is getting warmer”, said Dave Willard, director of honorary collections at the Field Museum in Chicago, who worked on measurements of all migratory birds.